A multiple-input multiple-output (MIMO) communication system is proposed as a wireless communication system that improves the transmission speed by using spatial multiplexing or that achieves high reliability by using the diversity effect that uses different propagation characteristics of multiple paths. In the MIMO communication system, for example, a wireless communication apparatus (e.g., a transmitter) with multiple antennas can simultaneously transmit data by using the antennas, and a wireless communication apparatus (e.g., a receiver), which is the other end of the communication, can simultaneously receive the data by using multiple antennas.
In an MIMO communication system, there are multiple communication methods for single user (SU)-MIMO communication, multiuser (MU)-MIMO communication, MIMO ad hoc multihop communication, cooperative multi-point (CoMP)-MU-MIMO communication, and the like. For example, in an SU-MIMO communication system, a single receiver has multiple antennas and uses the antennas to receive data that is transmitted from the multiple antennas of a transmitter. Thus, it is possible to achieve advantages, such as an increase in the data communication capacity and an improvement in the reception quality.
In the MIMO communication system, if the number of antennas used is increased, a large amount of data is transmitted and received to perform a process. As a result, the size, cost, and power consumption of circuits, or the like, connected to the antennas are increased, and the complexity of the overall MIMO communication system is also increased.
In an MU-MIMO communication system, or the like, where data is concurrently transmitted to multiple receivers that each include one or more antennas, it is desirable to perform a task of selecting or scheduling the antennas of a transmitter and a receiver (i.e., a user) that transmit and receive data to and from each other.
For example, Japanese Laid-open Patent Publication No. 2009-159377 discloses a technology for selecting a pair of transmitting and receiving antennas to be used from all the antennas so that the cost, complexity, power consumption, and the like, can be reduced.
As the complexity of an MIMO communication system is increased, the number of pairs of transmitting and receiving antennas becomes enormous. Even if the conventional method is used to select transmitting and receiving antennas, as disclosed in the above document, there is a technical problem in that a huge amount of processing time is required to select the optimum pair of antennas because of the increase in the number of pairs of antennas.
There is a conventional method for selecting a pair of antennas in which an inverse matrix is calculated from the matrix of a transmitting and receiving antenna set and the inverse matrix is used as a selection criterion. As the number of pairs of antennas is increased, the complexity of the calculation of the inverse matrix is increased, which results in an increase in the above-described processing time.